Sample vaporizing apparatus

ABSTRACT

An apparatus for vaporizing liquid samples containing impurities comprising a sample vaporizing and vapor receiving member having a surface portion thereof heated above the Leidenfrost point. The vaporized sample is drawn by a vacuum to a mass spectrometer for analysis through a passageway in the member that opens to the heated surface portion. Impurities in the sample remain in the liquid phase.

United States Patent [191 Thurston Aug. 7, 1973 SAMPLE VAPORIZING APPARATUS [75] Inventor: Warren M. Thurston, Deep River,

Ontario, Canada [73] Assignee: Atomic Energy of Canada Limited,

Ottawa, Ontario, Canada [22] Filed: July 29, 1971 [21] Appl. No.: 167,297

[30] Foreign Application Priority Data Oct. 16, 1970 Canada 095770 [52] US. Cl 250/413 S, 73/23.1, 73/4215 R,

250/288, 250/289 51 Int. Cl. 1-10lj 39/34 [58] Field of Search 13/31; 73/23.1, 421.5 R;

[56] References Cited UNITED STATES PATENTS 3,431,451 3/1969 Brunnee et al. 250/419 X 3,498,107 3/1970 Kim et al. 73/23.1

FOREIGN PATENTS OR APPLlCATlONS 161,568 8/1964 U.S.S.R 250/419 Primary ExaminerWilliam F. Lindquist Att0rney.lames R. Hughes [57] ABSTRACT An apparatus for vaporizing liquid samples containing impurities comprising a sample vaporizing and vapor receiving member having a surface portion thereof heated above the Leidenfrost point. The vaporized sample is drawn by a vacuum to a mass spectrometer for analysis through a passageway in the member that opens to the heated surface portion. Impurities in the sample remain in the liquid phase.

5 Claims, 4 Drawing Figures 7 PATENIEDMJG us-rs FIG. 2.

FIG.4.

SAMPLE VAPORIZING APPARATUS This invention relates to a liquid sample vaporizing apparatus and more particularly to a vaporizing device for water samples to facilitate determination of deuterium content thereof by mass spectrometric analysis.

A common known method for the preparation of liquid samples for mass spectrometric analysis consists of completely vaporizing a certain amount of liquid in a sealed container and thereafter introducing the vapor unto a mass spectrometer for analysis by methods similar to those used for gas analysis.

With the previous methods it is difficult to analyze a large number of samples quickly. In the production of heavy water it is desirable that a large number of samples from a variety of water sources be analyzed quickly to determine the deuterium content thereof.

My earlier U.S. Pat. No. 3,681,598 issued Aug. 1, 1972 describes a vaporizing device which facilitates automated analysis and which comprises a tubular mem ber for inserting into the sample having a reduced inlet bore, a tapered evaporation portion and an outlet for communication with a mass spectrometer and a vacuum source. This apparatus is suitable for the rapid analysis of liquid samples which are relatively clean. Samples containing a considerable amount of impurities, such as dissolved salts and suspended solids require time consuming cleaning procedures before this method can be successfully used.

The present invention provides a sample vaporizing apparatus which is suitable for liquid samples containing impurities such as dissolved salts and suspended solids as is found in sea water for example. The invention utilizes the Leindenfrost Phenomenon characterized by film boiling of a liquid adjacent to a metal surface heated above the Leidenfrost point (the temperature above which the liquid no longer wets the metal). Impurities in the liquid sample adjacent to the heated metal surface remain in the liquid phase while a representative sample of vapor can be withdrawn for analy- SIS.

The invention consists of a sample vaporizing apparatus comprising a sample vaporizing and vapor receiving member, means for heating a surface portion of the member above the Leidenfrost point, and a vapor conducting passageway extending from a substantially central portion of the surface portion to an outlet for communication with a vacuum source and a sample analyzing device.

In one embodiment the sample vaporizing apparatus comprises a tubular vaporizing member having a convex vapor receiving end, means for heating the convex end above the Leidenfrost point, the tubular member defining a vapor conducting passageway extending from a substantially central portion of the vapor receiving end to an outlet for communication with a vacuum source and sample analyzing device.

Preferably the apparatus includes at least one sample container having means for heating the sample to a temperature less than the boiling point for degassing.

In another embodiment the invention consists of a sampling apparatus comprising a vaporizing plate member having a concave sample receiving portion means for heating the plate member above the Leidenfrost point, a vapor conducting passageway in the plate member extending from a substantially central portion of the sample receiving portion and extending to an outlet for communication with a vacuum source and a sample analyzing device.

Embodiments of the invention will now be described with reference to the accompanying drawings wherein:

FIGS. 1 to 3 are partially cross-sectional views of three embodiments of the invention.

FIG. 4 is a schematic view of an embodiment for automated sampling.

Referring to FIG. l the apparatus comprises a tubular vaporizing member 10 having a convex vapor receiving end 11. The member 10 has heating means in the form of an electric heating element 15 for heating the end 11 above the Leidenfrost point. The tubular member defines a passageway 12 extending from a substantially central portion of the end 11 to an outlet 14. The passageway 12 defines a cavity for receiving a capillary intake probe 16 which is connected to a vacuum source and an analyzing device such as a mass spectrometer or chromatograph (not shown).

The sample 17 is contained by a depression 8 in a sample containing member 18 having heating means 13 for heating the sample to a temperature less than the boiling point for degassing.

The embodiment of FIG. 2 has a direct connectio from the passageway 22 to a vacuum source and analyzing device by means of the conduit 26.A restriction 29 in the end of the passageway limits the intake of vapor.

In FIG. 3 the sample vaporizing and receiving member is in the form of a plate member 30 having a concave sample receiving portion 31 for containing a sample 37. Heating means 35 maintains the surface 31 above the Leidenfrost point. The vapor is drawn by capillary probe 36 through a vapor conducting passageway defined by a restricted portion 39 and bore 32.

Preferably the plate member 30 has a sloping degassing channel 38. An inlay of non-corrosive material such as gold 33 covers the sample contacting surfaces.

FIG. 4 shows a schematic view of apparatus for auto mated sampling including a rotary sample changer 48, a sample vaporizer 40 a sample analyzing device 50 such as a mass spectrometer, a control valve 52 and a vacuum pump 51.

In operation, with reference to FIG. 1, the sample 17 is placed in the containing member 18 which is heated by heating means 13 to a temperature of approximately C to degas the sample removing dissolved air or gas which otherwise may prevent stable operation. Degassing is evident by bubbles appearing in the sample.

Next, the tubular vaporizing member 10, heated to a temperature of from 300 to 400 C, is lowered into the sample 17. A stable steam film 7 is formed around the end II. The liquid 17 is held away from the tip by the laminar flow of steam 7 produced by the heat from the vaporizing member 10. The laminar steam flow inhibits the mechanical transfer of dirt particles into the passageway 12. When the sample has been properly degassed the vapor film 7 is stable and vapor is formed in a quiescent manner with no ejection of salts which remain in solution in the liquid phase.

A vacuum applied to the capillary probe 16 draws a portion of the vapor produced to the analyzing device. The outlet 14 of vaporizing member 10 is larger than the capillary probe 16 to facilitate the free flow of the vaporized samples through the passageway.

In FIG. 2 the sample 17 is contained by a conventional container 28. The sample may be degassed by heating prior to placing in the container 18 or by heating in the container by any suitable means. In this embodiment the vacuum source is connected directly to the passageway 22. The withdrawal of vapor is limited by the restriction 29 to prevent air from being drawn into the passageway 22. Also, rapid withdrawal of the vapor may interfere with the formation of a stable steam film.

Referring to FIG. 3, a drop of the sample is placed into the degassing channel 38 at the outer edge of the plate member 30. As the sample contacts the heated member 30 it becomes heated and the dissolved gas is driven off so that the sample when deposited in the concave sample receiving portion 31 will be clear and stable. The drop of sample 37 will float on a steam cushion. The vapor to be sampled is vented downwards passing through restriction 39 and passageway 32. The vapor sample is withdrawn by a capillary probe 36 in a manner similar to that described above with reference to FIG. 1.

FIG. 4 shows schematically an apparatus for automated sampling incorporating a rotary sample changer 48. The sample changer 48 includes a plurality of depressions 41 for receiving the samples. The samples may be degassed prior to placing on the sample changer 48 or the sample changer may be heated to approximately 90 C to degass the samples as they are placed in the depressions 41. The automated cycle begins with the vacuum pump on and with the control valve 52 open. The vaporizing member is lowered onto one of the samples and after allowing sufficient time for a uniform vapor flow to be established the valve 52 is closed and the analyzing device 50 is dosed. Subsequently, the vaporizing member 40 is withdrawn and the valve 52 is opened to purge the vaporizing member and the analyzing device 50. The sample changer is rotated to move a new sample into position and the above cycle is repeated.

EXA'IWPTET With reference to FIG. 1, the preferred embodiment of the invention consists of a nickel vaporizing member having a diameter of 6 mm and a steam inlet 9 of 0.5 mm. The end 11 is hemispherical but slightly flattened over the central area to provide the best stability of the steam film 7.

Maximum penetration of water by the vaporizing member 10 before break down of the steam film is approximately equal to the diameter of the vaporizing member 10. Any visual penetration is sufficient to exclude the intake of air with the steam. Total air exclusion occurs before surface distortion can be visually detected.

With the sample containing member 18 heated to 90 C and with a sample size of 0.5 cc the degassing time is approximately 10 seconds.

The optimum operating temperature of the end of the vaporizing member was found to be 300 C to 400 C i The tip of the capillary intake probe 16 preferably has a diameter between 0.020 and 0.030 mm. The vacuum applied is preferably between 0.040 and mm hg. These values may be varied provided that steam is not removed from the outlet passageway 14 faster than it can enter passageway 9.

It was found that the precision of the system when standard intercomparison were made was better than i 0.1 ppm at natural deuterium concentration. An absolute error of about 0.3 ppm was noted when compared with total sample evaporation techniques. However, this error is a constant percentage for a given temperature of the water sample and can be corrected for by standard comparison along with other errors inherent in the mass spectrometer approach to D/H analysis (cg. Hf ion formation).

The above apparatus was found to be suitable for salt concentrations up to l0 percent.

E'X AMFITE 11 With reference to FIG. 3 the vaporizing plate member 30 has an inlay 33 of gold to prevent corrosion. Temperatures of from 175 to 350 were found to be suitable for the plate member 30. A suitable diameter for the passageway restriction 39 was from 0.1 to 0.6

Degassing of the sample by placing the drop in the degassing channel 38 occurs in from 0.5 to 2.0 seconds. After deposited in the sample receiving portion 31 it is found that the temperature of the drop is stable at about 8890 C regardless of the size of the drop or the temperature of the hot plate.

Satisfactory results were obtained with salt content up to 1 percent. However it was necessary to clean the plate member after 40-60 dirty samples because of deposits on the degassing channel 38. To extend the sampling time several degassing channels may be used. Stainless steel is suitable in place of gold but requires a increase in operating temperature for good degassing characteristics due to its lower thermal conductivity.

It will be understood that modifications may be made to the embodiments shown without departing from the present invention. For example, the heating means need not necessarily be as shown in the drawings but may be any suitable means that provides the required temperature. Also, a linear sample changer may be substituted for the rotary sample changer shown in FIG. 4. Further, with reference to FIG. 3, a direct connection from the passageway 32 to the vacuum source as in FIG. 2 may be substituted for the intake probe 26. p

I claim:

1. A liquid sample vaporizing apparatus comprising: a sample container, a tubular vaporizing member having a convex sample contacting metal surface portion, means for heating the surface portion of said member to a temperature above which the liquid no longer wets the metal of the member, said vaporizing member having a vapor conducting passageway opening to a substantially central portion of said surface portion, means for positioning said vaporizing member to contact the sample, a vacuum source communicating with said vapor conducting passageway for drawing off a portion of the sample vaporized by said heated vaporizing member, and means for restricting the flow of vapor drawn off by said vacuum source.

2. The apparatus of claim] further comprising means for heating said sample to a temperature less than the boiling point for degassing.

3. The apparatus of claim 2 comprising a plurality of sample containers, means for advancing said containers for successive sampling, and means for lowering and raising said tubular member in synchronism with said advancing containers.

the liquid no longer wets the metal of the member, said plate member having a vapor conducting passageway opening to a substantially central portion of the concave surface portion, a vacuum source communicating with said vapor conducting passageway for drawing off a portion of the sample vaporized by said heated concave member and means for restricting the flow of vapor drawn off by said vacuum source. 

1. A liquid sample vaporizing apparatus comprising; a sample container, a tubular vaporizing member having a convex sample contacting metal surface portion, means for heating the surface portion of said member to a temperature above which the liquid no longer wets the metal of the member, said vaporizing member having a vapor conducting passageway opening to a substantially central portion of said surface portion, means for positioning said vaporizing member to contact the sample, a vacuum source communicating with said vapor conducting passageway for drawing off a portion of the sample vaporized by said heated vaporizing member, and means for restricting the flow of vapor drawn off by said vacuum source.
 2. The apparatus of claim 1 further comprising means for heating said sample to a temperature less than the boiling point for degassing.
 3. The apparatus of claim 2 comprising a plurality of sample containers, means for advancing said containers for successive sampling, and means for lowering and raising said tubular member in synchronism with said advancing containers.
 4. The apparatus of claim 1 wherein the passageway of said tubular member defines a cavity for receiving a capillary intake probe, said probe being in non-sealing relation with said opening and connected with said vacuum source and a sample analyzing device.
 5. A liquid sample vaporizing apparatus comprising a vaporizing plate member having a concave metal sample receiving portion, means for heating the surface portion of said member to a temperature above which the liquid no longer wets the metal of the member, said plate member having a vapor conducting passageway opening to a substantially central portion of the concave surface portion, a vacuum source communicating with said vapor conducting passageway for drawing off a portion of the sample vaporized by said heated concave member and means for restricting the flow of vapor drawn off by said vacuum source. 